Do I need to explicitly set expected return values on Mock object only?

Is my observation correct:

public intercafe IMyInterface { bool IsOK {get;set;} }

// If I use stub this always return true:
var stub = MockRepository.GenerateStub<IMyInterface>();
stub.IsOK = true;

// But if I use MOCK this always return false -NOT开发者_运维技巧 True
var mock= MockRepository.GenerateMock<IMyInterface>();
mock.IsOK = true;

If I am right; why is the reason?

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The short answer is that you can set mock.IsOK to return true by setting an expectation on it and providing a return value:

var mock= MockRepository.GenerateMock<IMyInterface>();
mock.Expect(x => x.IsOK).Return(true);

Of course, to understand why, it helps to understand the difference between mocks and stubs. Martin Fowler does a better job in this article than I could.

Basically, a stub is intended to be used to provide dummy values, and in that sense Rhino.Mocks allows you to very easily arrange what you want those dummy values to be:

stub.IsOK = true;

Mocks, on the other hand, are intended to help you test behavior by allowing you to set expectation on a method. In this case Rhino.Mocks allows you to arrange your expectations using the following syntax:

mock.Expect(x => x.IsOK).Return(true);

Because a Mock and a Stub serve two different purposes they have entirely different implementations.

In the case of your Mock example:

var mock= MockRepository.GenerateMock<IMyInterface>();
mock.IsOK = true;

I wouldn't be surprised if the implementation of the IsOK setter on your mock is empty or ignoring your call completely.

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You've not specified for the mock that it should store the value and return that value, so it's just returning the default value of a bool. I'd say the reason for the difference in behaviour is because there is an implied difference between mocks and stubs in terms of usage, intent and behaviour.

Have a bit of a read-up on the differences between mocks, stubs and fakes. Not everyone agrees on a single answer, but you'll see there's a general consensus. Starting here might help: What's the difference between faking, mocking, and stubbing?